24

Season 1 is great, probably the best, I just finished watching Season 2 It's absolutely great, I'm getting Season 3 soon. Season 7 should be bad ass
 
I've seen season 1, got 2 on DVD but not watched it yet, seen some of 3 which wasn't that great, all of 4 and 5 but none of 6.
 
I have the seasons on my HD but I actually still have to watch the last 3 episodes from season one so I'm not too excited about the serie